1. Field of the Invention
The present invention relates to an ink jet recording apparatus for recording images by discharging recording liquid (ink) droplets from the recording head for its adhesion to a recording material. The invention also relates to a fixing heater to be used for such apparatus.
2. Related Background Art
An ink jet recording apparatus is utilized for a printer, a copying machine, a facsimile machine, a textile printer, and a plotter, among some others. The ink jet recording apparatus has a number of advantages in that it can print at high speeds even on an ordinary paper sheet, and that it can easily print in color. Therefore, the ink jet recording apparatus has been in use widely and increasingly along with the higher speed processing made available by use of personal computers in recent years.
Meanwhile, ink absorbing speed is slower for recording on an ordinary paper sheet than on a specially treated paper whose ink absorption is made faster. As a result, image unevenness tends to take place due to the non-uniformity of the recording surface of ordinary paper sheets. Also, the ordinary paper sheets are supplied by paper manufacturing companies in various places in the world. Therefore, the absorption of ink varies greatly by the variations of materials and methods of manufacture. Particularly, when color images are recorded, the amount of ink to be used is greater than that for a monochromatic recording, which requires a longer time for fixation. For improved recording on an ordinary paper sheet, it should be an effective means if the fixation of ink is promoted by the application of heat to the recording sheet. As the so-called "heating fixation" techniques where a recording material and recording liquid are heated for fixation, there have been developed, among some others, a hot plate heating method wherein a recording material is allowed to be in contact with a hot plate, a hot air method where hot air is blown onto recording liquid, a radiation heating method where a recording material is heated by the application of radiant heat using an infrared lamp, an infrared heater, or the like. For these conventional arts, a number of methods are proposed in which each of the heat fixation methods described above is used individually. However, along with the wider use of color recording in recent years, there are many examples in which the above-mentioned heating means are combined for use particularly as a countermeasure to cope with the increased recording duties.
In the specification of U.S. Pat. No. 5,020,244, a recording liquid fixing apparatus is disclosed in which a hot air heating and a radiant heating are combined. The techniques disclosed for this apparatus are such that energy saving is implemented for heating devices by circulating most of the hot air in the circular path arranged in the positions of heating devices, and also, in the carrier path of a recording sheet. In the specification of U.S. Pat. No. 5,428,384, a heater blower system is disclosed for use with a color ink jet printer. This system is such that by the combination of an air blasting and exhaust means, together with a radiant heating method, it is intended to produce a better recording of a higher quality with the evaporation of ink droplets adhering to a recording material, while effectively removing the vapor thus generated.
In the specification of Japanese Patent Laid-Open Application No. 8-258254, there is disclosed the means in which heating means using a heat roller, and blowing means are provided for heating a recording sheet to make it possible to apply heat to the recording sheet before and after printing by the provision of a large contact angle for the recording sheet with respect to the circumferential surface of the heat roller, at the same time, making it possible to blow air from below and above in the same direction as the carrying direction of the recording sheet, thus removing the vapor to be generated, and at the same time, cooling the recording head.
As an individual means of heating fixation, there is disclosed in the specification of U.S. Pat. No. 5,479,199, a radiant heating method wherein a reflection plate is provided for a wire heater, and a recording medium is heated from the reverse side thereof immediately under printing. In the specification of Japanese Patent Laid-Open Application No. 5-338126, a method is disclosed for heating and drying a sheet by the application of hot air from the reverse side thereof. Also, in the specifications of Japanese Patent Laid-Open Application No. 7-195683 and Japanese Patent Laid-Open Application No. 7-314661, means is disclosed for preventing ink from running and suppressing the deformation of paper sheet (crinkling and curling) resulting from the operation of ink jet recording.
However, in accordance with the conventional examples described above, the adoption of any one of them, such as the hot plate heating plate type, the hot air heating type, the radiant heating type, the heating method in which the hot air and radiant heating are combined, or the microwave heating type, may bring about excessive power dissipation, but the anticipated effect of image quality enhancement is still insufficient, even with the application of heat. It is still difficult for any one of them to cope with the higher speed requirement, the lowered image quality due to the vapor generation, and the larger size of the fixing device itself, among some other problems.
The hot plate heating method in which a recording material should be in contact with a hot plate is of a conduction and heat transfer type. Therefore, rapid heating is difficult, thus making it impossible to meet the higher speed requirement of late. Also, it is impossible to follow the changing condition of contact between the hot plate and the recording material, thus resulting in the drawback that image unevenness is generated.
For the hot air heating method in which hot air is blown onto the recording material, it is necessary to provide a measure to avoid condensation resulting from vapors contained in the hot air. This invites higher costs inevitably. Particularly when this method is adopted for an apparatus that uses the aqueous ink often used for ink jet recording, the generated water vapors bring about condensation in the interior of the recording apparatus, thus corroding electric parts or causing the short circuit thereof. Further, when blowing air to the printed surface, fine ink droplets tend to spread, and cause the degradation of image quality after all. Also, when blowing air to the reverse side of the printed surface, there is a need for the provision of air blocking means for the portions that do not require any heating. As a result, there is a problem that it becomes difficult to make the apparatus smaller.
The conventional radiant heating method uses an infrared lamp or an infrared heater as heating means. However, it is necessary to arrange a reflection plate in order to converge infrared rays to the region where recording is made. As a result, there is a problem that it becomes difficult to make the apparatus smaller. Also, since ink is heated by the infrared rays that should transmit the recording sheet, the heating effect on ink becomes insufficient. The anticipated enhancement of image quality is also insufficient accordingly.
The heating method in which the hot air and radiant heating are combined should require most of the hot air to circulate in the circulating path. As a result, the hot air becomes more moisture-laden as recording progresses. After continuous use, condensation takes place to allow the drops to adhere to the recorded images, thus staining the images or corroding electric parts to cause them to be short circuited or the like.
An ink jet recording apparatus, which is provided with the air blowing and exhausting means combined with the radiant heating method, is capable of instantaneously evaporating ink adhering to the surface of a recording material (paper sheet), thus preventing images from being degraded due to the permeation of aqueous ink into the paper sheet. However, the ink droplets adhering to the recording region are caused to spread by the draft from blowing means. Hence, ink mist flies to spread in the blowing direction and adheres to the circumference of recorded images, leading to the degradation of their quality. Also, if a larger image should be recorded with a larger amount of ink needed for it, the generated water vapors become fog that spreads outside the printer, hence producing unfavorable effects, such as condensation, on the peripheral equipment of the printer.
The recording system disclosed in the specification of U.S. Pat. No. 5,479,199 has a problem that this system cannot be utilized for a smaller printer, because not only the water vapor generation is insoluble, but also, the system cannot be made more compact.
The microwave heating has a considerable effect on aqueous ink. However, there is a problem of the water vapor generation. There are also problems of safety with respect to the human body, as well as of a greater dissipation of electric power. With these in view, this type of heating is not suitable for an ink jet printer for personal use.
Also, the ink jet recording apparatus, which is disclosed in the specification of Japanese Patent Laid-Open Application No. 57-120447, is capable of effectively heating paper pulp, polymeric substance, inorganic filler, ink solvent, or the like by means of a heating and drying device using the far infrared rays whose wavelength is 4 .mu.m to 400 .mu.m. Also, in the specification thereof, the far infrared rays whose maximum value of radiant energy intensity is at around 3.5 .mu.m are disclosed as usable for such apparatus. However, if the far infrared rays of this kind are used, both the recording paper sheet and ink are heated, making it impossible to effectuate any heating fixation that may render a good efficiency. Here, only 50% of moisture can be dried at a sheet feeding speed of 0.5 cm per second.
Further, in the specification of Japanese Patent Laid-Open Application No. 2-182461, it is disclosed that recording sheet and ink are intensively heated and dried by use of far infrared rays having the wavelength of 2 .mu.m to 1,000 .mu.m. However, an ink jet recording apparatus of this kind also heats both the recording paper sheet and ink after all. Also, there is no disclosure in the specification as to the spectrum data on the far infrared rays, which should specifically indicate the radiant energy intensity.